Safety Threshold Determination for Blasting Vibration of the Lining in Existing Tunnels under Adjacent Tunnel Blasting

Table 6

The peak stress of key point on the existing tunnel lining.

Simulated condition	Stress	Peak stress of key point (MPa)
		Arch crown	Blasting facing-side				Blasting backside
			Arch feet	Sidewall	Haunch	Spandrel	Arch feet	Sidewall	Haunch	Spandrel
III-grade rock mass	Tensile stress	0.57	0.67	0.38	0.44	0.48	0.56	0.37	0.40	0.43
	Compressive stress	0.53	0.54	0.40	0.42	0.39	0.56	0.46	0.48	0.51
IV-grade rock mass	Tensile stress	0.36	0.36	0.17	0.20	0.26	0.43	0.17	0.19	0.32
	Compressive stress	0.31	0.23	0.18	0.20	0.23	0.41	0.19	0.27	0.25
V-grade rock mass	Tensile stress	0.29	0.32	0.14	0.21	0.31	0.26	0.14	0.24	0.24
	Compressive stress	0.33	0.35	0.18	0.17	0.29	0.29	0.15	0.24	0.24
Control standards		1.10 MPa (compression strength design value for C20 concrete); 9.60 MPa (tensile strength design value for C20 concrete)